Hostile party (5)
(Other definitions for foe that I've seen before include "Evil rival" , "Antagonist" , "opposing side" , "Am archaic enemy" , "Someone opposing" .)
'hostile party' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for enemy that I've seen before include "Antagonist" , "Yemen (anag.)" , "Opposing force" , "Foe, adversary" , "Armed adversary" .)